Portable and wearable wireless devices and systems that operate from batteries require low power operation to extend the battery life. A radio frequency power amplifier (RFPA) is the most power hungry block of a wireless system. A switching RFPA is the most power efficient for constant envelope modulation such as Bluetooth and GSM. The desire to increase output power forces designers to use the battery voltage as the supply voltage for the power amplifier, which, in turn, requires utilizing IO devices as cascodes of the main switching core devices. The use of cascode devices adds significant power losses due to their parasitic capacitances and lower transconductances relative to the core devices.
FIG. 1 is an example cascode power amplifier 10 as known in the prior art. Referring to FIG. 1, a cascode power amplifier 10 includes a first transistor M1 and a second transistor M2 connected in series, i.e., the first transistor M1 has a drain connected to a source of the second transistor M2 and a source connected to ground. The second transistor M2 has a drain coupled to the battery supply voltage Vbat through an inductor L and a gate coupled to a voltage Vcasc which can be the battery supply voltage Vbat. The first transistor M1 operates as a common-source amplifier and the second transistor M2 operates as a common-gate amplifier. An RF input signal Vin is applied to a gate of the first transistor M1. The output signal Vout of the second transistor M2 has a full voltage swing from zero to Vbat and is provided to an antenna via a matching network. However, the cascode power amplifier 10 requires a high voltage manufacturing process. The high voltage transistors have a large parasitic capacitance resulting in high switching losses.
Therefore, there is a need for novel power amplifier configurations and methods that are applicable to high voltages and high frequency applications to decrease the power loss and noise behavior of the prior art.